Simple PRG subroutines of the universe may not necessarily be easy to
find. For instance, the second billion bits of 's dyadic expansion
``look'' highly random although they are not, because they are computable
by a very short algorithm. Another problem with existing data may be
its potential incompleteness. To exemplify this: it is easy to see the
pattern in an observed sequence
.
But if many
values are missing, resulting in an observed subsequence of, say,
7,
19, 54, 57, the pattern will be less obvious.

A systematic enumeration and execution of all candidate algorithms
in the time-optimal style of Levin search [#!Levin:73!#] should find
one consistent with the data essentially as quickly as possible.
Still, currently we do not have an a priori upper bound on the search
time. This points to a problem of falsifiability.

Another caveat is that the algorithm computing our universe may somehow
be wired up to defend itself against the discovery of its simple PRG.
According to Heisenberg we cannot observe the precise, current state of
a single electron, let alone our universe, because our actions seem to
influence our measurements in a fundamentally unpredictable way. This
does not rule out a predictable underlying computational process whose
deterministic results we just cannot access [#!Schmidhuber:97brauer!#]
-- compare hidden variable theory [#!Bell:66!#,#!Bohm:93!#,#!Hooft:99!#].
More research, however, is necessary to determine to what extent such
fundamental undetectability is possible in principle from a computational
perspective (compare [#!Svozil:94!#,#!Roessler:98!#]).

For now there is no reason why believers in S should let
themselves get discouraged too quickly from searching for simple
algorithmic regularity in apparently noisy physical events such
as beta decay and ``many world splits'' in the spirit of Everett
[#!Everett:57!#]. The potential rewards of such a revolutionary
discovery would merit significant experimental and analytic efforts.